FSX works fine since the last installation. Only the FSDT Stuff is not working.
Your issue doesn't have anything to do with FSX, it's a problem with Windows libraries, and the FSDT stuff is the VICTIM of your corrupted/missing Windows libraries which are, as I've said, the C++ runtimes and the Simconnect, NOT the cause.
One of them is causing this ( assuming it's not your antivirus or the Compatibility setting ) and since there might be several versions and sub-versions of a specific release, you can't be easily mislead it's an "FSDT problem" because "it doesn't happen to other software", but this it's JUST because other modules you are using might use a SLIGHTLY different version of those libraries that, by chance, is NOT corrupted in your system.
Yes, are MANY different version of, for example, the VC++ 2005 runtime library, and they can ALL run together (that's the whole point of the Windows Side-by-side system ), but if ONE of them has a problem, it will cause ONLY the products that are linked specifically against THAT specific build of the library, that's why you are MISLEAD believing the problem is that software, but it's not, it's that specific library release.
Simconnect it's another Side-by-side library, and on a normal FSX system with SP2, you'll have 3 VERSIONS installed at the same time, and that's normal, but if just ONE of them has problems, it would affect ONLY FSX add-ons that requires THAT specific version so, again, you can be mislead the problem is THAT specific add-on, when it's not, the real problem is your Windows installation or, more precisely, what happened in your Windows installation when you installed FSX, because it's the FSX installer that does all the work of registering those libraries in the system.
And of course, since they are (the VC++ libraries, not Simconnect) SYSTEM libraries, used by hundreds of other software, entirely unrelated to FSX, they CAN be corrupted by any other software you have installed, even if it doesn't have anything to do with FSX.
Again, that's what the REPAIR option in FSX and FSX SP2 try to do: to REPAIR a possible damage to its needed files, caused by ANOTHER program, even entirely unrelated to FSX:
WHICH IS WHY, I told you do to that.
I have few stuff installed and dont wont to repair the FSX.
You'll have to do it anyway, sooner or later, as soon you'll discover ANOTHER add-on that by chance would require exactly the same released of the libraries.
Again, assuming the OTHER TWO solutions I've posted (about DEP and UAC ) won't fix it, and assuming it's not your antivirus. It won't be the first time we heard of antivirus so defective, that is blocking programs even when you configure it to ignore them.
And, please, about the antivirus, follow the instructions TO THE LETTER. It's NOT enough to "just" configure it. You must TURN IT OFF, entirely, when DOWNLOADING AND INSTALLING.